1. Field of the Invention
The present invention relates to a recording material detecting apparatus and an image-forming apparatus.
2. Description of the Related Art
In an image-forming apparatus, such as a copying machine and a laser printer, that forms an image on a recording material (recording paper) by transferring and fixing a developer image based on an electro-photographic system, it is preferable to set various image forming conditions according to the size and type (paper type) of the recording material. For example, it has been known that transfer conditions (e.g., transfer bias, conveying speed of recording material during transfer) and the fixing conditions (e.g., fixing temperature, conveying speed of recording material during fixing) are set according to the size and type of the recording material which have been set by the user via a control panel or the like.
A technique proposed lately is to identify a size and a type of recording material using a sensor that detects the recording material in the image-forming apparatus, and setting the transfer conditions or fixing conditions according to the identified result. Japanese Patent Application Laid-Open No. 2004-38879 discloses that the surface smoothness is determined by imaging the surface of the recording material using a CMOS sensor.
According to the technique of imaging the surface of the recording material using such an image sensor as a CMOS sensor, a shading generated due to the unevenness of the surface is directly captured. However in the case of identifying standard office paper, for example, the shading generated due to the unevenness of the surface is often different depending on the fiber orientation direction (machine orientation) when the paper is manufactured. In other words, if light is irradiated from a direction perpendicular to the fiber orientation direction of the paper, a high contrast image is acquired where the unevenness state on the surface is enhanced. If light is irradiated from a direction the same as the fiber orientation direction, shading due to the unevenness does not appear easily, and a low contrast image is acquired. In other words, the identification result changes in some cases even if the same paper is tested, depending on whether the paper is fed vertically or horizontally.
In Japanese Patent Application Laid-Open No. 2004-38879, identification accuracy is improved by irradiating light diagonally with respect to the paper conveying direction. However the fiber direction of paper does not always match with or is not always perpendicular to the conveying direction, and in some cases the surface condition of paper, of which fibers are oriented in the diagonal direction with respect to the conveying direction, is identified as the surface characteristic of the paper itself.
Therefore, in Japanese Patent Application Laid-Open No. 2010-266432, light is irradiated onto a recording material in two different directions which are not parallel when viewed in a normal line direction of the surface of the recording material, using two independent light sources, shading on the surface of the recording material irradiated with the light in each direction is imaged, and two types of acquired images are used so that influence of the fiber orientation direction, with respect to the conveying direction of the recording material, is reduced and identification accuracy is improved.
In the technique of Japanese Patent Application Laid-Open No. 2010-266432, however, the two light sources are used to irradiate light onto the recording material in two different directions which are not parallel when viewed in the normal line direction of the surface of the recording material. But in the case of using two light sources, the directivity of the illuminance distribution of each light source may not be symmetrical. If this is so, light is irradiated onto the surface of the recording material in two different directions and the light quantity distribution in two areas to be imaged becomes asymmetrical, whereby an error may be generated when the image identification processing is performed.